1. Field of the Invention
The present invention relates to mobile communications systems and, in particular, to a device and method for eliminating an interference signal in a mobile communication system.
2. Description of the Related Art
Recently, due to the rapidly growing demand for mobile communication, much attention has been directed to Code Division Multiple Access (CDMA) as a means for performing such communication. There are two types of CDMA systems. The first type is referred to as Direct Sequence CDMA or DS-CDMA, which is an application of spread spectrum technology. The second type is referred to as Frequency Hopping CDMA or FH-CDMA. In Korea, a digital DS-CDMA communication system has been developed and is currently in service. Additionally, DS-CDMA is currently being used in Korea for Personal Communications Services (PCS) systems.
In the above DS-CDMA system, diminished performance is primarily caused by multipath fading and multi-user interference (MUI), which, in turn, are caused by multipath propagation and the simultaneous use of the same channel by multiple users, respectively. Thus, stated alternatively, the performance of a DS-CDMA system can be improved by mitigating the effects of multipath fading and MUI.
Multi-user interference is generally reduced by the following two techniques: using an adaptive array antenna; and co-channel interference cancellation based on correlation. The use of an adaptive array antenna allows for the effective removal of an interference signal by appropriately controlling the antenna""s directivity. However, this technique is limited in eliminating an undesired signal received at the same angle as that of a desired signal. On the other hand, the co-channel interference cancellation technique generally assures the removal of MUI, thereby improving system performance. However, mitigation of co-channel interference requires a PN (Pseudo Noise) code which exhibits excellent correlation characteristics, and an interference canceller. System hardware complexity increases with the number of users that simultaneously access the system because undesired spread spectrum signals from all users are demodulated, re-spread, and then extracted from a received signal in order to recover a desired signal using a digital filter.
To solve the problems of the above techniques, there is a need for a receiver having an adaptive array antenna and an interference canceller which are serially connected. An adaptive antenna and an interference canceller were used in the prior art as a way to increase DS-CDMA system capacity. However, such use was not employed in a CDMA environment where they should be serially connected, but rather, such use occurred in a general spread spectrum communication environment. In this context, it is difficult to make a direct application of the conventional devices to a CDMA system.
An object of the present invention is to provide a receiver and a receiving method in a radio communications system, which can increase reception performance by use of an adaptive array antenna and an interference canceller which are serially connected.
According to one aspect of the invention, a receiver in a mobile communications system is provided. The receiver includes: an adaptive array antenna having a plurality of antenna elements for forming a beam in the direction of a desired signal, each of the plurality of elements having an adaptive linear filter associated therewith; a real time adaptive receive processor for controlling beam patterns and directions of the plurality of antenna elements at a reception angle of the desired user; and an interference canceller operatively connected to said adaptive array antenna for detecting a multi-user interference signal from the desired signal and cancelling the multi-user signal.
According to another aspect of the invention, a receiving method in a mobile communications system is provided. The method includes the steps of: controlling beam patterns and directions of an adaptive array antenna to coincide with a reception direction of a desired signal; forming a beam in the reception direction of the desired signal; and eliminating an interference signal received at a different angle than the reception angle of the desired signal.